| Potash fertilizer is the one of three kinds of necessary fertilizers in agriculture widely. The reserve of soluble potash resources is lack and the distribution of that is imbalance seriously in China. Comparatively, there are abundant and comprehensive insoluble potash resources in our country. It is important to research and develop new processes and technologies of potassium extraction from local insoluble ore with potassium and utilize the main components in ores comprehensively, which can solve current serious problems of the shortage of soluble potash resources in China effectively and bring economic and social benefits.Chemical composition, mineral components and contents, mineral association and mineral grain size distribution of potassium-rich shale from Chaoyang of Liaoning was studied by means of scanning electronic microscope (SEM), EDS, x-ray diffraction (XRD), thermal analysis (DTA), ICP, infrared spectrum(FT-IR), and mineral liberation analyzer (MLA). Occurrence state of potassium in potassium-rich shale was determined. Main minerals with potassium in the shale were potassium feldspar, muscovite, illite, biotite and a small number chlorite and the main gangue mineral was quartz. About 80% of potassium in the shale exited in the potassium feldspar and there was 20% of potassium in such mica with potassium as muscovite, illite and biotite.According to the basic principle of crystal chemistry and valence-bond theory, characteristic parameter of chemical bond and crystal structure of main silicate minerals with potassium in the shale were calculated and analyzed. The results showed that chemical properties of the Si-O bond and Al-O bond of the skeletal structure of microcline and muscovite were stable relatively. Potassium in silicate crystal structure was stably attached to oxidize by ionic bond.Processes of potassium extraction from potassium-rich shale were studied in the pyrolytic system and the hydro-thermal system respectively. Furthermore, mechanisms of potassium exraction were determined.Two different kinds of pyrolytic techniques were used on the base of different alkali-treated mode-roasting the mixed materials after preprocessing potassium-rich shale with NaOH and roasting potassium-rich shale directly with KOH. Main influence factors on potassium extracting rate in the both of pyrolytic procedures were studied. The results showed that the former potassium extraction ratio was 88.08% and the latter was up to 99.99% under optimum conditions. And under the latter optimum conditions, aluminum removal ratio of filter residue was 97.6% and silica hydrated with good micro-properties was obtained.The mechanism of potassium extraction in the both of roasting techniques, roasting mixed materials after preprocessing potassium-rich shale with NaOH at mass ratio of NaOH to shales being 0.7 and roasting mixed materials at mass ratio of KOH to shales being 1, was studied by XRD, SEM and TG-DSC, respectively. The research results showed that the mechanism of potassium extraction in pyrolytic process was disintegrative course of silicate minerals with potassium gradually under the action of alkali. The decomposition products of silicate minerals with potassium were diverse, due to different alkali-treated modes and use level of alkali in the both of pyrolytic techniques. The former mechanism was that such insoluble minerals with potassium as potassium feldspar and mica in the shale were turned into acid-soluble kaliophilite under high temperature and a little bit alkali, and kaliophilite became the main phase in roasted products. However, the latter mechanism was that potassium feldspar and mica with potassium in the shale were melted and disintegrated to form such soluble phase with potassium as K2SiO3 and K2Al2O4. Calculation and analysis of thermodynamics showed that main chemical reactions in two different kinds of pyrolytic processes could perhaps occur. The analysis of kinetics determined that both of pyrolytic processes were controlled by diffusion and model equations were in accordance with dynamical equation of Crank-Ginstling-Braunshtein.The acidic mechanism of roasted products in both of pyrolytic techniques during the process of acid-leaching was studied by XRD and SEM. The acidic mechanism of roasted products after roasting mixed materials with NaOH at 600℃was that under acidic condition, kaliophilite with potassium was dissolved to form K+, Al3+etc. And, by the theory of double electrode layer, The acidic mechanism of roasted products after roasting mixed materials with KOH at 700℃was that under the action of Excessive acid, K2Si03 turned into colloidal silica, and then colloidal silica was agglomerated to produce precipitate of SiO2·nH2O.The research results of influnces of main factors on potassium extraction in hydro-thermal system showed that potassium extraction ratio was up to 95%under optimum conditions. By XRD and SEM analysis for leaching residue and transition state theory, the mechanism of potassium extraction in hydrothermal system was that minerals with potassium in potassium-rich shale were decomposed and turned into new products and potassium in raw samples entered into solution as K+. Calculation and analysis of thermodynamics showed that main chemical reactions in the system could perhaps occur. The analysis of kinetics determined that the model equation to be controlled by chemical reaction was abtained.According to the above experimental results and mechanism analysis, this paper put forward the technical proposal of comprehensive application of potassium-rich shale in both of pyrolytic and hydro-thermal system. Silica hydrated, K2SO4, Al(OH)3 and Fe2O3 could be produced in the processes of comprehensive application of potassium-rich shale with KOH by pyrolytic method, which met the requirements of national standards. During processes of hydrothermal reaction, potassium in potassium-rich shale could form K2CO3 product and the leaching residue was a kind of cement padding.In this paper, the characteristics of potassium-rich shale from Chaoyang of Liaoyang and the processes of potassium extraction were determined. The research results were important to develop and practise continuable utilization of resources with potassium. |
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